INCLUSION APPENDAGES ASSOCIATED WITH THE INTRAERYTHROCYTIC RICKETTSIAL PARASITE ANAPLASMA-MARGINALE ARE COMPOSED OF BUNDLED ACTIN-FILAMENTS

Anaplasma marginale, a tick-borne rickettsia that infects erythrocytes of cattle, occurs within a parasitophorous vacuole or inclusion body. A tail-like inclusion appendage, composed of multiple filaments, occu rs in association with the inclusion body membrane. The composition an d function of the inclusion appendage have not been determined. In thi s study, the A. marginale inclusion appendage in bovine erythrocytes w as found to be composed of actin filaments as determined by labeling w ith rhodamine-conjugated phalloidin. Electron microscopy studies revea led that the A. marginale inclusion appendages differed from F-actin t ails reported previously in association with other pathogens in eukary otic cells because these highly ordered structures were organized into regularly occurring striations, and the appendages were adhered direc tly to the parasitophorous vacuole membrane. In addition, actin append ages have not been described previously in erythrocytes. The potential role of the inclusion appendage associated with A. marginale in bovin e erythrocytes and recently fed ticks is discussed.